1. Field of Invention
The techniques described herein relate generally to determining the perceptibility of noise in images. Noise reduction techniques may be applied based on the perceptibility of the noise.
2. Discussion of the Related Art
Digital images and video may be transmitted over a channel in numerous applications, for example, the transmission of digital television signals. In some applications, the digital images and video may be compressed before transmission to increase the amount of information that may be transmitted. For example, if digital television signals are compressed, a greater number of television channels may be transmitted than without compression.
The compression of digital images and video may be lossless or lossy. Where the compression is lossless, the original images or video may be exactly reproduced after decompressing the data. Where the compression is lossy, however, the original images or video may not be reproduced exactly, and may have “noise” caused by the lossy compression algorithm. In some applications, lossy compression may be preferred to lossless compression because the compression rates may be greater.
The compression of images and video may add different types of noise. One example of noise is “blocking” noise. An image or frame of video may be divided into a plurality of blocks. Some compression algorithms, such as MPEG, may process blocks of image and video, and differing effects around block borders may cause noise to appear. Other types of noise that may occur include “ringing” and “mosquito” noise. Ringing and mosquito noise may appear near sharp edges in an image and may create noisy artifacts that extend spatially and/or temporally away from a sharp edge.
In some applications, techniques may be applied to reduce the appearance of decompression noise. For example, filters may be use to reduce ringing noise in images and video. Applying techniques to reduce noise, however, may also adversely affect the non-noisy portions of an image or video. For example, using a filter to reduce noise can blur regions of an image and reduce the quality with which the details of an image can be reproduced.